This invention generally relates to intravascular catheters, such as balloon dilatation catheters used in percutaneous transluminal coronary angioplasty (PTCA).
PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon dilatation catheter is advanced into the patient""s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient""s artery to open up the arterial passageway and thereby increase the blood flow there through. To facilitate the advancement of the dilatation catheter into the patient""s coronary artery, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique through the brachial or femoral arteries. The catheter is advanced until the preshaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery, and the distal tip of the guiding catheter is then maneuvered into the ostium. A balloon dilatation catheter may then be advanced through the guiding catheter into the patient""s coronary artery until the balloon on the catheter is disposed within the stenotic region of the patient""s artery. The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not over expand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference.
To properly position the balloon within the stenotic region, the balloon must be advancable within the patient""s tortuous vasculature. Additionally, the balloon must be advanced across the stenosis, typically referred to as the ability to cross the stenosis. However, the design of balloon catheters must balance the competing concerns of flexibility and balloon softness required for trackability and crossability with balloon strength and low compliance required to expand against the stenosis.
Therefore, what has been needed is a balloon catheter with improved trackability, crossability and strength. The present invention satisfies these and other needs.
The invention is directed to a balloon formed of a single layer of a substantially unblended copolymer having a flexural modulus of at least 150 kpsi (1 GPa). A single layer is defined as one layer of copolymer used to manufacture the balloon. The copolymer is a copolymer of polybutylene terephthalate (xe2x80x9cPBTxe2x80x9d) and polytetramethylene ether glycol terephthalate (xe2x80x9cPTMEGTxe2x80x9d).
In a presently preferred embodiment, the copolymer is substantially unblended with any other material. Substantially unblended, for the purpose of this patent is defined as greater than about 60% by weight of the copolymer. In a more preferred embodiment, the balloon is formed of no less than about 95% by weight of the copolymer. The most preferred embodiment is about 100% by weight PBT and PTMEGT copolymer. Suitable polymeric materials for blending with the PBT and PTMEGT copolymer include polymers such as polyethylene terephthalate or polybutylene terephthalate to make a stiffer balloon.
A balloon catheter of the invention generally comprises a catheter having an elongated shaft with proximal and distal ends, an inflation lumen, and a single layered balloon formed of a copolymer made of polybutylene terephthalate and polytetramethylene ether glycol terephthalate. A suitable PBT and PTMEGT copolymer includes Hytrel(copyright) polymers from E.I. DuPont de Nemours and Company. Hytrel(copyright) is available in a range of grades. Properties of the grade are determined by the ratio of PTMEGT to PBT. The presently preferred copolymer is Hytrel(copyright) 8238, which has a shore durometer hardness of 82D.
In accordance with the invention, the balloon is formed of a polymeric material, whether 100% copolymer or substantially unblended, the polymeric material having a flexural modulus of greater than about 150 kpsi (1 GPa). The flexural modulus is a measure of the ratio of stress to strain during flexural deformation. Therefore, a high flexural modulus number means a material is harder to distort with increasing force. Preferably, the copolymer has a flexural modulus of at least 175 kpsi (1.17 GPa).
The material will have an elongation at break of at least about 200%, preferably about 350% or higher. The tensile strength of the material at break will be at least 5500 psi, preferably greater than about 6500 psi (45 MPa). The tensile strength for the most preferred material is about 7000 psi (48 MPa) or higher. The balloon made from the material will have an average rupture pressure of at least 18 atm, and is usually about 22 atm to about 26 atm for a balloon with a double wall thickness of about 0.0016 inches (0.04 millimeters).
The balloon of this invention will have a low compliance. The term complaint is understood to mean the measure of the increase in diameter of the balloon under pressure. Low compliance is meant to imply radial expansion less than about 0.045 millimeters per atmosphere of pressure applied (mm/atm). In the most preferred embodiment of the invention, the resulting balloon has a compliance of less than 0.02 mm/atm within the working range of the balloon of about 10 atm to about 18 atm.
Various designs for balloon catheters well known in the art may be used in the catheter of the invention. For example, the catheter may be a conventional over-the-wire dilatation catheter for angioplasty having a guidewire receiving lumen extending the length of the catheter shaft from a guidewire port in the proximal end of the shaft, or a rapid exchange dilatation catheter having a short guidewire lumen extending to the distal end of the shaft from a guidewire port located distal to the proximal end of the shaft. Additionally, the catheter may be used to deliver a stent mounted on the catheter. balloon.
The balloon of the invention provides improved performance because of the strength of the material coupled with its unexpected tracking and crossing ability. The catheter of the invention has the unexpected ability to track as well as a catheter with a balloon formed of a more compliant material with a lower flexural modulus. Tracking is the ease that the balloon catheter moves through the blood vessel and advanced over the guidewire. Good tracking ability means the user feels less resistance. In addition, the balloon of this invention could cross a lesion which Nylon and Pellethane balloons known in the art could not cross. The balloon of this invention, once deflated, also had the ability to recross the lesion after initial dilation. Therefore, the balloon of this invention would make an excellent choice for physicians dealing with multiple stenosis and re-dilation cases.
The material properties of the balloon also make the invention ideal for stent implantation. The balloon has low compliance, coupled with high pressure capability. Therefore, the balloon of this invention would be used for a balloon catheter to cross a non-dilated lesion and expand to simultaneously dilate the lesion and implant the stent.
These and other advantages of the invention will become more apparent from the following detailed description of the invention and the accompanying exemplary drawings.